1. Field of the Invention
The present invention relates to a torque estimating device for estimating the drive torque of a compressor.
2. Description of the Related Art
Since the past, the compressor for a vehicular use air-conditioning system has obtained its drive force from the vehicle engine. In this type of vehicle, in general, the drive torque of the compressor is estimated and the estimated drive torque is used to control the engine output so as to prevent fluctuation of the engine speed even if the drive torque of the compressor changes. For this reason, suitable estimation of the torque of the compressor is an important task.
From this background, it is known to successively switch the torque estimating means after startup of the compressor so that a startup stage torque estimating means estimates the torque of the compressor in the initial period after startup of the compressor and a stable stage torque estimating means estimates the torque of the compressor in the steady state and thereby enable suitable estimation of the torque in accordance with the stage after compressor startup (for example, see Japanese Patent Publication (A) No. 2006-272982).
Japanese Patent Publication (A) No. 2006-272982 utilizes the property that the high pressure side pressure of the refrigeration cycle rises and peaks somewhat delayed from the actual rise of the torque of the compressor at the time of startup to deem that the startup of the compressor has been completed when the rise of the high pressure side pressure becomes 0 or less and switches the torque estimating means of the compressor accordingly. However, since the timing of switching the torque estimating means of the compressor is not based on the actually measured value, the precision of estimation deteriorates due to the delay of the switching timing.